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| Titel |
Downhole fluid sampling and noble gas analysis of saline waters from the Outokumpu Deep Drill Hole, Finland |
| VerfasserIn |
Thomas Wiersberg, Riikka Kietäväinen, Lasse Ahonen, Ilmo Kukkonen, Samuel Niedermann |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250088659
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| Publikation (Nr.) |
 EGU/EGU2014-2796.pdf |
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| Zusammenfassung |
| The 2516 m deep Outokumpu Deep Drill Hole is situated at the NW-SE trending boundary
between the Archaean and Proterozoic domains of the eastern Fennoscandian Shield
(Finland). In August 2011, eight fluid samples were collected with a Leutert positive
displacement sampler (PDS) from 500 m to 2480 m depth in the open bore hole. The PDS
allows sampling at in situ pressures, thus minimising fractionation from degassing during
sampling. At the surface, the samples were transferred into an evacuated sampling line
connected with a Cu-tube and a glass bulb for gas sampling, a pressure gauge, and a
thermometer. Gas was liberated with a heated ultrasonic bath and then admitted to the
sampling devices. Gas/water ratios were already determined in the field during gas
extraction.
Saline groundwaters rich in methane, nitrogen, hydrogen and helium and with water
stable isotope composition distinctive from meteoric and sea water have been found to host
isolated ecosystems within the Precambrian crystalline bedrock of Outokumpu
(Kietäväinen et al., 2013). In order to characterise the geochemical and microbiological
evolution of the deep subsurface of the area, noble gas residence times have been
calculated based on radiogenic (4He, 40Ar), nucleogenic (21Ne) and fissiogenic (134Xe,
136Xe) noble gas nuclides. Geochemical and microbiological variations together
with hydrogeological and geophysical data indicate negligible vertical fluid flow
in the bedrock. Moreover, noble gas diffusion models show that diffusion is not
likely to affect noble gas concentrations of groundwater at or below 500 m depth in
Outokumpu. Therefore in situ accumulation was assumed as a basis for the age
determination. In general, residence times between 10 and 50 Ma were indicated by 4He
and21Ne, while somewhat younger ages were obtained by 40Ar, using average values
for porosity, density and concentration of radioactive elements in the bedrock of
Outokumpu.
Kietäväinen R., Ahonen L., Kukkonen I.T., Hendriksson N., Nyyssönen M. and Itävaara
M. (2013),Appl. Geochem. 32, 37-51. |
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